The present invention relates to an apparatus for holding a stack of sheets and for dispensing the sheets one at a time. More particularly, this invention concerns a cassette for holding a stack of unexposed photographic-film sheets.
A stack of photographic sheet material held in a cassette is normally displaced out of the cassette, a sheet at a time, after exposure of the topmost sheet by sliding this topmost sheet laterally off the stack and out through a slot in the end of the cassette. In order to insure proper positioning of the sheet in the focal plane of the camera in which the cassette housing is to be fitted, the stack of sheets in the disposable cassette are usually held against a window in the front of the cassette by means of a plate which is pressed toward this window by means of a compression spring which is braced between this support plate and the sidewall of the housing opposite that wall that is formed with the window.
In order to maintain best planarity of the topmost or end sheet of the stack it is necessary to press it with considerable spring pressure against the windowed wall of the housing. The greater this spring pressure is, however, the harder it is to slide the end sheet off the stack. Thus the spring force is often made to be less than that force which would achieve best planarity in order to be able to readily pull out the exposed upper sheet.
Another disadvantage of the known cassettes, particularly in arrangements having self-developing film, is that more than one of the sheets occasionally is ejected at a time. Since the sheets are normally pulled out between a pair of pressure rollers, the extra ejected sheet must be discarded, as it is rendered useless once it is pulled out of the cassette. This accident is particularly likely to happen when the spring force urging the stack against the windowed wall of the cassette is great.